The disclosures herein relate generally to a heart valve prosthesis particularly to a tilting disc valve having one or more leaflets.
Tilting disk valves have an advantage over translating disk valves in that the side profile of a tilting disk or leaflet is thin and unobstructive when rotated to the open position compared to the translating disk or ball type valve. The minimally obstructed passage of blood through an open tilting leaflet valve reduces the amount of work required by the human heart employing such a valve.
An example of a translating disk valve is disclosed in U.S. Pat. No. 3,725,961 wherein a prosthetic heart valve is disclosed having a support ring which carries means for retaining a movable closure element in positions adjacent one side of the ring. The support ring has a fabric wrapping which defines, as a suturing element, an annular protrusion of fabric of double thickness extending from the side of the ring which is opposite the side adjacent the closure element.
U.S. Pat. No. 3,476,143 discloses a one-way mechanical heart valve comprising a base having a passage allowing liquid to flow through the valve. A disc located within the passage pivots about a chordal axis to an open position and a closed position relative to a seat on the inside of the base. In one form the seat includes an inclined upper arcuate seat and an inclined lower arcuate seat circumventing the passage. In another form, the seat is an annular portion of the internal annular wall which is engaged by the periphery of the disc. Two pairs of circumferentially spaced pivot projections provide for the pivoting of the disc about a cordial axis of the disc. Retaining means in the form of curved side ears or a center strut hold the disc in assembled relation with the base.
U.S. Pat. No. 3,698,018 discloses a heart valve prosthesis having a discoid poppet mounted therein for pivotal movement between a closed and opened position. The poppet is supported for movement by opposed, spaced support struts which form an eccentric pivot point for opening of the valve and a changing pivot point for closing of the valve. The spacing between the struts is sufficient to enable rotational movement of the poppet during operation.
U.S. Pat. No. 4,276,658 discloses a heart valve prosthesis coated in its entirety with pyrolytic carbon. The prosthesis is formed of a base having a blood passageway and dual leaflets pivotally secured to the base to regulate the flow of blood through the passageway. The pivot connection between the base and leaflets is formed by recesses in the base and projections on the leaflets, the recesses and projection termini being formed as surfaces of revolution. The valve is assembled by elastically deforming the base to allow insertion of the projections within the recesses.
U.S. Pat. No. 4,443,894 discloses a heart valve having a pair of leaflets which are supported by respective floating pivots. The pivots guide the leaflets between open and closed positions due to the leaflets being pivotally mounted in dog-leg shaped depressions. The depressions each have a downstream section which angles outward from a centerline plane of the valve body and a connected vertical upstream section. In the closed position, the guides reside in intermediate portions of the depressions to unload wear forces between the guides and the depression walls for reducing wear on the pivot points.
U.S. Pat. No. 4,689,046 discloses a heart valve prosthesis with an annular body portion and at least one valve leaflet moveable between open, closed, and intermediate positions. The body includes leaflet ear support formations, each with a contoured recess having spaced apart convex ear support surfaces. Each valve leaflet includes mounting ears with upper and lower support surfaces of generally trapezoidal outline, a generally flat end face portion, and two spaced apart guide surface portions tapered so as to lie in closely spaced apart relation to the tapered guide walls in the recess.
U.S. Pat. No. 5,147,390 discloses a bi-leaflet heart valve having an annular body and a pair of leaflets. The leaflets pivot around improved ears, whose motion is constrained by generally triangular recesses. The triangular recesses have a pivotal vertex in proximity to a centerline of the annular base and on the upstream side of the heart valve. Opposite the pivotal vertex is a slightly convex base. The opening angle of the leaflets can be adjusted by varying the inclination of a wall of the triangular recess adjacent the center line. The opening angle should be adjusted, according to the teachings of the present invention, to minimize energy loss for a particular inside diameter of the heart valve. The optimum opening angle can be determined by in vitro testing using an adjustable valve and a pulse duplicator.
U.S. Pat. No. 5,824,062 discloses a bi-leaflet heart valve including an annular base and pivoting leaflets. Each leaflet is "free-floating" within recesses without fixed rotational axes, to increase translational movement and redistribute stresses. Each recess fluidly communicates with a groove extending at least partially around the inner surface of the annular base and flow is directed through the recesses at different angles during antegrade circulation, retrograde circulation, and valve closure. A recess entrance angle to each of the recesses is preferably less than about 35.degree., and the pivoting mechanism within the recess includes first and second fulcrum edges of each leaflet shiftably engaged with side surfaces of the respective recess. The leaflets have a beveled bottom surface having two separate planar surfaces which lie at an angle to one another. A central region of each leaflet is spaced apart from the annular base when the leaflet is in a fully closed position to minimize cavitation.
As it is well known, tilting leaflet heart valves operate in a rotational motion. These valves may include one leaflet, two leaflets (bi-leaflet) or possibly three leaflets. The leaflet rotates about an axis displaced from the centerline of the valve housing. When the leaflet rotates to a closed position in the housing, the contact between the leaflet and the housing usually occurs at a single point. As illustrated in the references above, some valves have a simple point contact along the housing wall and others have an overlapping surface contact.
The leaflets can fail due to cavitation. This occurs because the leaflet moves at a very high velocity as blood is pumped through the valve. The blood adjacent the valve closure point wants to continue to move after valve closure occurs. Thus, a low pressure region is created adjacent the valve contact point. If the low pressure region reaches a minus 760 mm Hg, i.e. 1 atmosphere, cavitation occurs creating a bubble in the blood which subsequently implodes causing cavitation erosion of any adjacent surface such as a surface of the valve. Factors involved with cavitation include the velocity of the moving leaflet and the valve contact geometry.
From a performance standpoint, it is desirable to have a valve which closes quickly to reduce the quantity of blood flowing in the retrograde direction. This is dependent on the velocity factor. The single point of contact between the leaflet and the valve housing occurs at the farthest distance from the axis of rotation of the leaflet. Therefore, the point of contact had the highest linear velocity of any point on the leaflet, thus increasing the likelihood of cavitation. The single point of contact is near the center of the peripheral edge of the leaflet, i.e. the leaflet major radius (MR).
Cavitation erosion occurs near the MR on the inflow side of the leaflet and at an adjacent location on the housing. The faster the leaflet is moving just before impact, the higher the rate of deceleration. When the leaflet decelerates too quickly, the inertia of the blood causes it to separate from the surface of the leaflet resulting in the above-described low pressure region and causing the bubble to form. Thus, the cavitation erosion damage occurs in a location which is downstream (during reverse flow) of the leaflet/housing orifice contact upon closure.
Therefore, in view of the limitations of past developments, what is needed is a tilting leaflet valve which moves the contact point away from the MR without an unacceptable increase in the amount of the leakage during valve closure.